The project focuses on the effects on the Navajo Indian Reservation of accessibility and availability of ambulatory care services on patterns of utilization of these services and on the health status of the user population problems of availability and accessibility are especially relevant concerns on the Navajo Indian Reservation where a population of 150,000 is scattered over an area of 25,000 square miles. The major hypothesis is that with decreases in accessibility or availability of ambulatory care services, utilization will also decrease. The data base will be a seven year collection of Indian Health Service ambulatory patient care reports on computer tapes. Two samples of the approximately 3/4 million records per year will be drawn; one from 1972 to be followed forward to 1978, and another from 1978 to be traced back to 1972. The seven IHS service units will be arranged on a continuum from more rural to more urban population and within each servie unit the distance of communities to the nearest hospital outpatient department, health center or health station will be measured. An additional sample of aggregate ambulatory data will be utilized for 1973, 1975 and 1978 data existing aggregate inpatient data for 1973 and 1978 will be utilized as a crosscheck to view the entire health care delivery system. Conditions which will be closely followed for trends will primarily be preventable diseases such as otitis media, trachoma, skin diseases and infant morbidity/mortality in general. High blood pressure will also be highlighted for examination as an indicator of the delivery system reaching and controlling cases. A second part of the study will be to examine the findings of the analysis for implications for planning of the ambulatory care delivery system.